Identification of relevant antigens in schistosomiasis and other parasitic diseases continues. The measurement of antibody responses to individual components of complex mixtures may reveal clinically relevant information obscured by responses to crude mixtures. Purification of a trichloroacetic acid (TCA-S-C) fraction of adult schistosomes led to the finding that the magnitude of antibody responses to specific antigens present in crude TCA-S-C correlated with clinically pertinent parameters whereas the responses to crude TCA-S-C failed to do so. Levels of antibodies to PSAP, a polydisperse glycoprotein, correlated with the egg excretion rate but the responses to gut associated proteoglycan (GASP) correlated with the acuteness of infection. Levels of antibodies as measured by a number of methods correlated well. Radioimmunoassays employing labelled antigens were more sensitive and specific than an ELISA test employing poly(L-lysine) coated plates. Excretory and secretory antigens of adult B. malayi have been identified by radiolabelling E-S products and using these labelled materials to measure antibodies in infected patients. Analysis of the mixture revealed a number of parasite antigens and some contaminating host products.